Automatic telephone-exchange system



June 24, 1930. E. H. CLARK E AL AUTOMATIC TELEPHONE EXCHANGE SYSTEK I Filed Sept. 29, 1923 10 shets sheet 1 5 h. CLARK W W GMPEA/Tffi A 7 TORNE Y June 24, 1930.

E. H. CLARK ET AUTOMATIC TELEPHONE EXCHANGE SYSTEM 10 Sheets-Sheet 2 Filed Sept. 29. 1928 QQN ATTORNEY I V 5/75 62AM W QARPEiVTEl-i June 24, 1930. 'ET AL 1,757,959

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W 14 CARPENTER A Tram/EV June 24, 1930. CLARK ET AL Efifilfi AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Sept. 29, 1928 1Q Sheets-Sheet 6 June 24, 19mm. E. H. CLARK ET AL 1,7 7,

AUTOMATIC TELEPHONE EXCHANGE SYSTBII Filed Sept. 29. 1928 0 Sheets-Shet '7 HUNDRED THOUSA N05 ATTUR/VD June 24, 1930.

.E. H. CLARK El Al}, I 1,767,959

AUTOMATIC TELEPHONE EXCHANGE $YSTEI I Filed Sept. 29, 1928 10 Sheets-Sheet ffi/ 5mm lNVE/VTOQS: v WW AfiPEA/TER ATTORNEY Jim: 24, 1930., .E. H. CLARK ET'AL" 1,767,959

'AUTOMATIC TELEPHONE EXCHANGE SYSTEI Filed Sept. 29, 1928 10 Sheets-Sheet 9 E H CLARK /Nl ENTOP$-' W W Q4RPENTR mat/M ATTORNEY June 24', 1930.- E. H. CLARK ET! AL 1,767,959

AUTOMATIC TELEPHONE EXCHANGE SYSTEM Filed Sept. 29,- 1928 10 Shgets-Shept 10 Patented June 24, 1930 EDGAR I-I. CLARK, on FOREST HILLS, AND WARREN lJthdSh w. CARPENTER, or Queens" VILLAGE, NEW YORK, ASSIGNORS T0 BELL TELEPHONE LABORATORIES, INCOB PORATED, OF NEVJ YORK, N. Y., A CORPORATION 0F NEW YORK AUTOMATIC TELEPHOI'JE EXCHANGE SYSTEM Application filed. September 29, 1928.

This invention relates to telephone ex change systems and particularly to those sys tems wherein mechanical switching apparatus is employed in the establishment of connections between subscribers lines termihating in manual oiiices of the exchange area and subscribers lines terminating in machine switching offices of the same area.

The invention has for its object the simplifieation of apparatus necessary for the establishment of such connections and the in creased economy in the first cost and maintenance thereof.

In exchange areas which are being changed through the installation of machine switching apparatus to operate on a full mechanical basis rather than on a strictly manual basis,

it is desirable that provision be made for the extension of calls originated in a manual oftice of the exchange to any of the outlying auton'iatie otiices through the control of the selector switches in the called automatic ofiice, by mechanism located at the calling manual ofiice. As the exchange area becomes more nearly full mechanical through the changing of a greater number of the manual oiiices to automatic olhces, the need for such control equipment for the remaining manual oiilces becomes more essential. By this plan the operator who first answers the call is enabled to establish the inter-oliice connection which leads to a distant automatic oliice without assistance, the entire operation of the switches at the distant automatic office being governed by mechanism at the origiotlice controlled bythe answering operator therein.

This has been accomplished satisfactorily in the past by circuits or" the type shown, for example, in Patent 1,513,862, issued October 28, 1924, to L. M. Allen. The present invention was developed toattain the same results as have been heretofore attained in the employment of circuits of the type disclosed in Serial No. 309,174.

this patent with simpler apparatus and with greater economy.

In accordance with the present invention, one embodiment of which has been disclosed herein, by way of. illustration, each manual oilice is provided with a plurality of operators positions, each of which has access to a plurality of groups of outgoing trunks, one

group leading to each of the automatic of fices of the exchange area. Each position is further equipped with a sender controlling keyboard, a set of ofiice keys, and ofiice code registers, and a set of relay registers and indicating'lamps for trunk identification purposes. In order that an idle sender common to all operators positions may be taken for use to extend a call and associated with the key board and registers of the operators position concerned, each position isprovided with two hunting switches, the first of which hunts for an idle sender to immediately associate the operators keyboard with the numerical registers of the sender, and the second of which assumes a similar setting from the first to extend additional control' ling conductors between the registers of the position and the sender. In order that the selected sender may become associated with an idle trunk to the desired automatic otlice, each sender is associated with a first selector switch individual thereto which in turn has access through second selector switches to all of the trunks in the difierent groups extending'tothe several automatic ofiices.

In the operation of the system, the operator who answers an incoming call at the originating manual office first depresses an oflice key at her position corresponding to the ollice in which the.desired line terminates and thereby causes the association of her position apparatus with an idle sender and the registration of the office code designation of the de sired line on the oilice code register relays of her position; She may then depress keys in her keyboard to register on the numerical registers of the sender the numerical designation of the desired line. The tens designation of the office code is then transferred to a code register in the sender and the first selector switch is set under sender control in accordance therewith, and thereupon hunts for an idle second selector to further extend the connection toward the desired interoffice trunk group. Thereafter the units designation of the office code is transferred to the code registers of the sender which is now instrumental in setting the second selector switch whereby a group of trunks to the desired office is selected. The second selector is operated further in hunting movements to find a subgroup of trunks to the desired office and an idle trunk in a selected sub-group, such selective movements being registered in the sender which in turn controls the setting of the trunk number indicating relays of the position apparatus to indicate to the operator the number of the selected outgoing trunk.

The operator then plugs into the jack of the indicated trunk and her position apparatus is freed for another call. The sender thenproceeds to operate the selector switches in the selected automatic office in accordance with the numerical designation of the wanted line registered on the registers thereof in the well known manner.

Referring to the drawings, Figs. 1 to 10 inclusive, arranged in accordance with the diagram of Fig. 11 disclose so much of a telephone system embodying the principles of this invention as is necessary to a comprehensive understanding thereof.

Fig. 1 shows one of a plurality of answering operators positions in a manual office provided with cord circuits for extending subscribers lines over interofiice trunks outgoing to distant dial switching offices. One of these outgoing trunks terminating in a dial switching office is illustrated in this figure.

Fig. 2 shows a set of numerical keys, two office keys and a portion of the office code register of the operators position shown in Fig. 1.

Fig. .3 shows sender selecting switch for associating the operators position equipment of Figs. 2 and 4t with the sender shown in Figs. 5, 6, 7 and 8.

Fig. 4 shows a trunk number indicating equipment for indicating to the operator the number of the interoffice trunk over which the connection to the desired dial switching office is to be extended, and a group of transfer relays.

Figs. 5, 6, 7 and 8 taken together show one of a plurality of register senders available for the use of all operators of one manual office. Fig. 5 shows two steering switches of the sender. Fig. 6 shows control relays. Fig. 7 shows relay registers for registering the numerical digits of wanted line numbers and Fig. 8 shows control and counting relays for setting the switches of the dial switching office under the control of the registers of Fig. 7 counting relays for controlling the setting of the trunk number indicating equip ment of Fig. l, and oifice code register relays.

Fig. 9 shows a first selector individual to the sender, and Fig. 10 shows one of a plurality of second selectors for connecting a selected sender with an idle trunk extending to a desired dial switching office.

Fig. 11 is a diagram showing how the various tion to each other.

The selector switches 123 and 12 i diagrammatically illustrated in Fig. 1 and located in the distant dial switching oifice 122 are of the well known power driven type such as are shown in the patent to E. B. Craft and J. N. Reynolds, No. 1,123,696, issued January 5, 1915. More particularly they are of the specific type fully disclosed and described in the patent to F. A. Stearn and F. J. Scudder, No. 1,395,977, granted Nov. 1, 1921.

The sender selector switches 300 and 350 and the steering switches 500 and 550 are of the rotary single motion step-by-step type driven by stepping magnets from terminal to terminal and so arranged that the brushes are moved forward to the next set of terminals upon the deenergization of the corre sponding stepping magnet. Switches 300 and 350 have no definite normal position.

The selector switches of Figs. 9 and 10 are of the step-by-step type having both a vertical and a rotary motion. Each switch is provided with a pair of brush sets and corresponding banks of terminals and each therefore has a capacity of 200 trunks. More specifically, these switches are of the type disclosed in the Patent No. 1,7 00,466, granted to W. l/V. Carpenter Jan. 29, 1929.

The operators position equipment shown in Fig. 2 comprises a set 211 of ten nonlocking digit keys upon which the operator may write up the numerical digits of wanted line numbers, a plurality of oifice keys only two of which 200 and 206 have been disclosed, and two groups of code register relays. As many office keys are provided at each operators position as there are dial switching offices in the exchange area to which the manual office has access. Each group of code register relays comprises eight relays, only the first and last of each such group having been disclosed in order to simplify the drawing. The register relays of one group register the tens code letter of an office designation and the relays of the other group register the units code letter. By suitable interconnections with the office keys it is possible by the depression of a sin gle key to register the first two letters of the olfice designation corresponding to such key. For example, as will be hereinafter more figures should be arranged with relaw fully described, the depression of key 200 registers the office code CA for the office GAnal'on the tens register relay 202 and on theunits register relay 201. Similarly the depression of key 206 registers the office designation AT for the oflice ATchinson on the tens register relay 207 and on the units register relay 201.

It is believed that the invention will be best understood from a detailed explanation of the manner in which a connection may be established. To this end it will be assumed that the subscriber of line 100 in the manual office wishes to converse with the subscriber of line 125 in a distant dial switching oiiice 122. Upon removing his receiver from the switchhook, the calling subscriber completes acircuit for the energization of line relay 104 which in turn causes the illumination of lamp 105. The operator upon observing the illumination of lamp 105 answers by inserting the plug 102 of one of her cord circuits in the jack 101. The insertion of the plug in the jack completes a circuit from battery through the lamp 107, resistance 106, sleeves of plug102 and jack 101, winding of relay 103 to ground. Relay 103 operates and severe the circuit of relay 104 which causes the line lamp-105 to become extinguished. The receiver being on the sWitchhook, the insertion of the plug in the jack also completes a circuit from battery through the lower left winding of repeating coil 100, the winding of relay 110, rings of plug 102 and jack 101, over the loop of the line returning over the tips of jack 101 and plug 102, upper left winding of repeating coil 109 to ground. Helay 110 operates in this circuit and closes a circuit from battery through its contact, resistance 108, resistance 106, thence over the path previously traced through the winding of relay 103 to ground. This latter circuit shunts the lamp 107 causing the same to remain extinguished.

The operator nextdepresses the listening key 112 connecting her headset into conversational relation with the calling line and ascertains the wishes of the calling subscriber. Upon learning that he wishes to talk with a subscriber at a distant office 122, the operator depresses the office key 200 of Fig. 2, which key corresponds to such distant office. For the purposes of this description it will be assumed that the wanted line numher is CAnal 398 and that therefore by the depression of key 200 the No. 2 units code register relay 201 and the No. 2 tens code register relay 202 are operated over a circuit extending from battery through the right wind- 7 ing of relay 201, the left Contact of key 200,

the right winding of relay 202 to ground at the right back contact of relay 203. Relays 201 and 202 both energize closing a mutual locking circuit for each other extending from battery through the left winding and inner left contact of relay 201, the left winding and inner left contact of relay 202, to ground at the left back contact of release relay 205. At its right contact key 200 closes a circuit from ground over the left back contact of relay 203 to battery through the winding of relay 204. Relay 204 operates and looks from battery through its winding, winding of relay 203, the front contact of relay 204 to ground at the outer right contact of relay 201. Relay 203 does not operate in this looking circuit until the key 200 is released since its winding is shunted by ground at the right contact thereof. Relay 203 upon operating opens the initial operating circuit of all register relays to prevent the operation of other register relays at this time. The code register relays prepare circuits for the transfer of the oliice code number to the sender as will. iereinafter be described.

Seizure of an idle sender The code relay 201 also establishes a circuit from. ground at its outer right contact over conductor 208 to battery through the winding. of relay 301. It will first be assumed that the set of terminals upon which the brushes of the sender selector 300 are standing is con nected with an idle sender. hen therefore relay 201 energizes, ground on conductor 208 is connected through the right winding of relay 307, the left back contact of relay 304, test brush 308 to battery through the winding of a relay corresponding to relay 501, Fig. 5, of such idle sender. Since full battery potential exists on the test terminal upon which the brush 308 is resting, relay 307 energizes and locks from ground at the left con tact of relay 301, the front contact of relay 307 to battery through its ri 'ht winding. At its normal contacts relay 307 opens the circuit for relay 304 thereby preventing the operation of relay 304 to close the circuit of stepping magnet 309. The selector 300 therefore" does not advance and the sender which is then connected to the set of terminals upon which the brushes thereof are standing, is taken for use. Since ground is now connected to the test terminal upon which the brush 303 is standing through the right winding of relay 307 from conductor 208, the potential on such test terminal is reduced to mark the sender as busy to other sender selectors.

Tt'will new be assumed that the sender connected to the first set of terminals of the selector 300 is busy and that the test potential encountered by brush 308 is reduced to such an extent that relay 307 does not energize. When therefore relay 301 operates, a circuit is established for relay 304 extending from ground at the left contact of relay 301, the normal contacts of relay 307, the right back contact of relay 306 to battery through the winding of relay 304. Relay 304 energizes and looks through its inner left front contact over brush 308, the test terminal upon which it is resting, the multiple thereof, brush 308 of another sender selector resting thereon, the right winding of relay 307 of the operators position connected with such busy sender to ground at such operators position. At itsinner right contact relay 304 closes an obvious self-interrupting circuit for magnet 309 which operates and advances the brushes of selector 308 to the next set of terminals. At its outer right front contact relay 304 closes a circuit extending from ground thereat over the left back contact of relay 303 to battery through lamp 302 for lighting the lamp. Lamp 302 glows steadily so long as the selector 300 is advancing in search of an idle sender. At its left back contact relay 304 opens the circuit of relay 307 to prevent its operation until after an idle sender has been found and at its outer left front contact relay 304 closes a circuit extending in parallel through the winding of time measure relay 306 and the winding of relay 310 to battery. Relay 310 upon energizing disconnects the key strip 211 from the brushes 312, 313, 314 and 315 to prevent the false operation of any sender registers should the operator through error depress a key while the brushes of selector 300 are passing over terminals associated with busy senders and connects the key strip 211 to battery through the left winding of relay 303. Should the operator at this time depress a key, relay 303 will operate to switch lamp 302 from steady ground to interrupted ground through the fast interrupter 316. The operator noting the flickering of lamp 302 is apprised of the fact that she has started to record the wanted line designation too soon.

Relay 306, which is slow to release, opens at its right contact the initial energizing circuit of relay 304. So long as the brush 308 encounters the test terminals of busy senders, relay 304 remains locked and the circuit of magnet 309 remains established thereby to continue the advance of selector 300. As soon as the terminals of an idle sender are encountered, which it will be assumed is the set of terminals appearing as the third set in the banks of selector 300, relay 304 will receive no locking ground and since relay 306 is holding its initial energizing circuit open, relay 304 will release opening the circuit of magnet 309. Relay 307 now energizes in the circuit previously traced from ground on conductor 208,

the right winding of relay 307, the left back contact'of relay 304, brush 308, conductor 334, to battery through the winding of relay 501 of the selected sender. Should two sender selectors simultaneously select the same sender and two relays such as 307 be connected in the previously traced circuit in parallel, neither relay 307 would energize and as soon as the time measure relay 306 releases the previously traced circuit of relay 304 would be again established to advance the selector 300 in search of another sender.

Upon the release of relay 306 and the energization of relay 307, a circuit is established from battery through the winding of relay 317, the back contact of stepping magnet 318 of selector 350, the back contact of relay 319, the left contact of relay 306, the front contact of relay 307 to ground at the left contact of relay 301. Relay 317 energizes and at its front contact extends its own operating circuit through the winding of stepping magnet 318. Magnet 318 energizes opening the circuit of relay 317 which releases in turn opening the circuit of magnet 318. Relay 317 and magnet 318 thus operate reciprocally to cause the step-by-step advance of the brushes of selector 350. When the selector has advanced to a position corresponding to the position assumed by the selector 300, a circuit is closed for relay 319 extending from battery through the winding of relay 319, brush 320 and terminal 321' of selector 350, conductor 322, terminal 323 and brush 324 of selector 300, the left contact of relay 306 and thence to ground as traced at the left contact of relay 301. Re-

la 319 energizes o aenin at its back contact the stepping circu1t of selector 350 to arrest its further advance and closing at its front contact a circuit for relay 325 extending from battery through the winding of relay 325, the front contact of relay 319, the left contact of relay 306, thence to ground as traced. Relay 325, at certain of its front contacts, connects the control conductors 331, extending to the sender selected by the selector 300 over the brushes 326 to 330 inclusive of selector 350 to contacts of the transfer relays associated with the trunk number indicator of Fig. 4. At its outer right contact relay 325 connects locking ground to conductor 332 for a purpose to be hereinafter described.

The lamp 302 is at this time disconnected from direct ground and connected over the left back contact of relay 303, the right back contact of relay 304, the right contact of relay 301 to ground through the interrupter 305, and lamp 302 flashes as an indication to the operator that an idler sender has been associated with her position apparatus and that she may proceed to set the sender registers to record the number of the desired line.

Relay 501 upon energizing prepares several circuits. At its outer left contact it connects ground to conductor 502 extending to battery through the winding of relay 700 and over brush 503 and the first terminal of steering switch 550 to battery through the winding of relay 504. Relays 7 00 and 504 both energize, relay 7 00 connecting ground to conductor 701 for furnishing locking ground for the register relays of Fig. 7 and also connecting ground over its lower contact to conductor 702, thence to battery through the winding of relay 915 of the first selector shown in Fig.

9. Relay 915 of the select or in turn connects holding ground for locking relays of the selector and opens at its back contact one point in the operating circuit of release magnet 917. Relay 504 upon energizing Connects locking ground to connector 508 for locking operated counting relays of Fig. 8. At its inner left contact relay 501 connects ground to conductors 509, 510 and 511 for furnishing locking ground to relays of Figs. 5, 6 and 8 and at its inner right-contact connects ground to conductor 801, thence through the winding of re lay 800, conductor 902, off normal contacts 901 of the first selector, thence to battery through the left winding of relay 900. Relay 900 operates in this circuit but relay 800 being low wound does not operate. Relay 900 upon 01 erating locks over its left front contact to ground at the front contact of relay 915 independently of the off-normal contacts 901, and prepares an'operating circuit for the vertical magnet 903. At its outer right contact relay 501 establishes a circuit extending from battery through the winding of stepping magnet 512 of steering switch 550, thence over conductor 513, outer right front contact of relay 504, conductor 506, the left back contact of relay 802, conductor 507, the outer right contact of relay 501, the normal terminal and brush 514 of switch 550, conductor 515 to ground at the outer left contact of relay 600. Magnet 512 energizes preparatory to advancing the brushes of steering switch 550 one step.

Setting code register for first 07,9506 code letter As soon as the sender selector 350 has been positioned circuits are effective for setting the relays 803, 804, 807 and 808 of the office code register of the sender. It will first be assumed that both a first and second selector such as shown in Figs. 9 and 10 are to be operated to select a trunk to the clesireddial switching office in response to the office code letters CA, the letter C corresponding to the digit 2. For this purpose the armature contacts of the tens oiiice code'relay 202 of Fig. 2 which was operated in response to the depression of the office key 200 are cross-connected in such a manner as tooperate the code register relay 804 of the sender over a circuit extending from battery through thewinding of relay 804, the outer right back contact of relay 805, conductor 806, brush 328 of selector 350, the inner left contact of relay 325, conductor 400, the intermediate left contact of transfer relay 401, conductor 402 to ground at the intermediate right contact of relay 202.

In order to register digits corresponding to all of the code letters used in ofiice codes, four register relays 808, 804, 807 and 808 are employed in the sender, which may be operated individually and in combination TC: over circuits extending in the manner previcontact of counting relay 814,

ously traced for relay 804 to grounded armature contacts of the code register relays of Fig. 2. To enable a better understanding of the manner in which the code digits may be registered in the sender the following chart has been prepared.

The vertical column of figures at the left of the chart indicates the digits corresponding to office code letters that may be registered by the office code relays. The numbers in the sub-divisions of the chart'opposite this vertical column indicate the relays of the sender register which are operated for the corresponding digits to be registered and'the numbers above each vertical column of the chart indicate the conductors of Fig. 2 which must be variously grounded by the register relays of Fig. 2 to operate theregisterrelays 0f the sender. 'lhus, digit 8 is to be registered, by reading horizontally across the chart it will beapparent that register relays 803, 804 and 807 must 'be operated in combination and that to operate these relays a code relay of Fig. 2 must be operated which will 402 and 403.

With the register relay'804 operated a ground conductors 405,

pulsing circuit extending from the first selector of Fig. 9 may be traced from battery, winding of relay 904, back contact of rotary magnet 905, back contact of vertical magnet 903, inner right back contact of relay 906, intermediate right back contact of relay 907, conductor 908, outer right back contact of relay 809, back contact of the counting relay 810, conductor 811, back contact of relay 601, winding of relay 602, inner left back contact of relay 600, left back contact of relay 603, conductor 604, left contact of relay 804, conductor 812, normal terminal of brush '514 of steering switch 550, conductor 515 to ground at the outer left contact of relay 600. Relays 602 and 904 energize in this circuit, relay 602 upon energizing closing a circuit from ground at its front contact, the right, back contact of relay 605, conductor 606, brush 516 and normal terminal of switch 550, conductor 517, right front contact of register relay 804, right back contact of register relay 803, counting'relay lead 813, right back winding of counting relay 832 to battery. Relay 832 energizes and locks through the winding of relay 814 over the front contact of relay 832 for example, if the i to ground on conductor 503, but relay 814 does not energize until relay 602 deenergizes and removes the shunting ground from its winding.

At the selector of Fig. 9 upon the energization of relay 904, a circuit is closed for the vertical magnet 903 from battery through the winding of magnet 903, the outer right front contact of relay 900 to ground at the inner left front contact of relay 904. Relay 904 also closes an obvious circuit for relay 909 which disconnects the tip and ring brushes of the selector during its vertical selection movement. Magnet 903 energizes and at its contact opens the previously traced pulsing circuit through the winding of relay 904 and the winding of relay 602. The selector switch is thus stepped vertically one step opening at the off-normal contact 901 the initial energizing circuit of relay 900. Upon the opening of the pulsing circuit and the deenergization of pulsing relay 602, the shunt around counting relay 814 is opened and such relay energizes in the locking circuit of relay 832 extending the counting relay lead 813 over its front contact, the back contact of counting relay 816, conductor 817, brush 518 and normal terminal of steering switch 550, conductor 519, the right back contact of register relay 807 to battery through the winding of counting relay 818. Relay 818 energizes upon the next closure of the pulsing circuit and the consequent energization of relay 602, and looks through the winding of relays 802 and 810 in parallel over the front contact of relay 818 to ground on conductor 508.

At the selector, relay 904 reenergizes and in the manner previously described causes the advance of the selector shaft another step, again opening the pulsing circuit. When the pulsing circuit is again opened and relay 602 deenergizes relays 302 and 810 energize, relay 810 opening the pulsing circuit extending as previously traced to the first selector, and relay 802 opening the previously traced circuit extending magnet 512. Magnet 512 now deenergizes advancing the brushes of steering switch 550 one step into engagement with the second set of terminals of the arcs. to which they have access.

WVhen the steering switch leaves position 1 the circuit of relay 504 is opened and such i relay releases removing ground from conductor 508 thereby releasing the operated counting relays. A circuit is now established for relay 603 extending from battery through the winding of said relay, conductor 608, the second position terminal and brush 503 of steering switch 550 to ground at the outer left contact of relay 501. Belay 603 energizes establishing a circuit for trans fer relay 401 extending from battery through the winding of such relay, the inner right through the winding of back contact of transfer relay 406, the intermediate right contact of relay 325, brush 326 of switch 350 and the terminal upon which it is resting, conductor 333, the intermediate left back contact of relay 607 to ground at the inner right contact of relay 603. Relay 401 operates closing a locking circuit for itself from battery through its winding, the winding of relay 406, the right front contact of relay 401, to ground on conductor 332. Relay 406 does not energize in this locking circuit, however, so long as relay 603 remains energized. At its back contacts relay 401 disconnects the conductors 402 to 405 inclusive, extending to contacts of the tens code register relays of Fig. 2 from the group of conductors 331 extending to the code register relays of the sender. The operated code register relay 804 thereupon releases.

With relay 504 deenergized a circuit is now established for relay 609 extending from battery through both windings thereof, the outer right back contact of relay 610, conductor 611, the back contact of relay 504, conductor 612, the right back contact of relay 600, conductor 613, the inner right back contact of relay 809, conductor 910, the outer right back contact of relay 907, the outer right back contact of relay 906, the inner right front contact and right winding of relay 900 which is wound difierentially to the left winding of such relay, commutator brush 911, to ground on terminal 912 of the commutator corresponding to the second vertical level of the lower bank of the first selector which level of terminals has been assumed to be connected to trunks" terminating in second selectors such as the one shown in Fig. 10. Relay 609 operates in this circuit and closes a circuit for relay 614 extending from battery, winding of relay 614, front contact of relay 609 to ground on conductor 510. Relay 614 upon operating shunts at its left front contact, the left winding of relay 609 which thereupon increases the current flowing through the right winding of relay 900, whereupon relay 900 differentially releases removing the vertical magnet 903 from the control of stepping relay 904. Relay 900 also connects the right winding of relay 609 over the circuit previously traced to the inner right back contact of relay 900 thence to battery through resistance 913 over the back contact of rotary magnet 905. Relay 609 thereupon releases and at its front contact opens the'previously traced circuit of relay 614. Since relay 614 is slow to release a circuit is momentarily closed upon the release of relay 609 from ground on conductor 510 overthe back contact of relay 609, the right front contact of relay 614 to battery through the winding of relay 610 which thereupon energizes and locks to ground at the intermediate right contact of relay 603.

Relay 610 upon energizing opens the circuit of relay 609 at its outer ri ht rack contact and at its outer right front contact closes a circuit for relay 615 extending from ground therethrough over the right front contact of relay 610, conductor 611, the back contact of relay 504, conductor 612, thence as traced to battery through resistance 913 at the first selector. Relay 615 operates in turn operating relay 616 over a circuit extending from battery through the Winding of relay 616, the left back contact of relay 605 to ground at the contact of relay 615. Relay 6 16 upon operating locks over its left contact to ground at the back contact of pulsing relay 602 and at its right contact establishes an obvious circuit for relay 617 Which relay in turn establishes a circuit for magnet 512 of the steering switch 550 extending from battery through the Winding of magnet 512 over conductor 513, the left back contact of relay 805, conductor 819 to ground at the left front contact of relay 617. Relay 617 also at its right contact closes an obvious circuit for relay 605.

A circuit is noW established for the stepping relay 904 of the first selector extending from battery through the Winding of relay 904, back contacts of rotary magnet 905 and vertical magnet 908, back contacts of relays 906 and 907, conductor 908, outer right back contact of relay 809, back contact of counting relay 8 10, conductor 811, back contact of rela 601, Winding of sender pulsing relay 602, inner left contact of relay 600, left front con tact of relay 603, the left front contact of relay 610, the right front contact of relay 605, conductor 632, the second position terminal and brush 514 of steering switch 550, conductor 515 to ground at the outer left contact of relay 600. Relays 904 and 602 operate in this circuit. Relay 9'04 upon energizing closes the circuit of relay 909 to disconnect the tip and ring brushes of the selector during its hunting movement and closes the circuit of rotary magnet 905,1Vl1i8l1 may be traced from battery through the Winding of magnet 905, the outer right back contact of relay 900 to ground at the inner left contact of relay 904. Magnet 905 upon energizing in turn opens the previously traced circuit for relays 904 and 602, relay 904 in turn opening the circuit of magnet 905. Thus relay 904- and magnet 905 cooperate With each other to cause the step-by-step rotation of the first selector brushes over the selected second level in search of an idle second selector.

At the sender upon the energization of pulsing relay 602 the holding circuit of relay 616 is opened at the back contact of relay 602 and relay 616 deenergizes in turn opening the initial energizing circuit of relay 617. Relay 617 being slow to release, however, does not release before a holding circuit is established therefor from battery through its Winding, the inner right front contact of relay 605 to ground at the front contact'of relay 602. Therefore as long as relay 602 con tinues to receive impulses of current due to the hunting movement of the first selector, relay 617 is held energized and in turn maintains relay 605 operated. Relay 615 isat this time deenergized since its operating circuit was opened at the back cont-act of rotary magnet 905 upon the first energization of magnet 905 and the initial operating circuit of relay 616 is therefore opened at the contact of relay 615.

1 V hen an idle second selector is found av circuit is established for relay 1015 extending from battery, Winding of relay 1015, conductor 916, terminal 919, brush 920, next to inner back contact of relay 909, conductor 921, back contact of relay 820, to ground on conductor 702. Relay 1015 energizes connecting locking ground for the relays of the second selector and opening at one point the circuit of release magnet 1017. Another circuit is also established from battery, through the left Winding of relay 1000, off-normal contacts 1001, conductor 1002, terminal 922, brush 914, outer left back contact of relay 906, the back contact of release magnet 17, inner right back contact and right Winding or relay 907, conductor 902, Winding of relay 800, conductor 801, to ground at the inner right front contact of relay 501. Relays 1000 and 907 operate in this circuit but due to its small number of turns relay 800 does not operate. Relay 1000 upon operating locks over its left contact to ground at the front contact of relay 1015 and at its outer right front contact prepares the operating circuit of the vertical magnet 1003. Relay 907 upon operating looks over its left front con tact to ground at the front contact of relay 915, at its left back contact opens the energizing circuit for relay 906, and at its inner right back contact opens its own initial energizing circuit, and connects the trunk conductors 908 and 9'10 over its outer and intermediate right front contacts, over right bacl: contacts of relay 909, ring and tip brushes 923 and 924 to the second selector trunk conductors 1008 and 1010. At its inner right front contact relay 907 connects ground on conductor 902, over lease magnet 917, the outer left back contact of relay 906, brush 914, terminal 922 to conductor 1002. At its intermediate right back contact relay 907 also opens the circuit previously traced through the windings of relays 904 and 602 Whereuponthese relays are released.

Pulsing relay 602 upon releasing opens the holding circuit of slow to release relay 617, which in turn releases relay 605. Relay 617 upon releasing also opens the circuit of magnet 512 Which advances the brushes of steering switch 550 into contact'with the third pothe back contact of re-.

' ma net 512 ener izes reoarator to advancb b A ing the steering switch another step.

It has been assumed that the second code letter registered on the coderegister relays of the operators position was A having a numerical equivalent of 2, and that the units register relay 201 was energized by the depression of key 200. The armature contacts of relay 201 are cross-connected to conductors 407 to 410 inclusive in such a manner that conductor 408 is grounded to operate the oilice code register relay 804 of the sender over a circuit extending from battery, through the winding of relay 804, the outer right back contact of relay 805, conductor 806, brush 328 of selector 350, the inner left contact or relay 325, conductor 400, the intermeciate left contact of transfer relay 406, the intermediate left front contact of transfer relay 411, con ductor 408 to ground at the inner right contact of relay 201. It is to be noted in this connection that the sender code register relays 803, 804, 807 and 808 are operated singly and in combination in accordance with the foregoing table over conductors 407 to 410 inclusive to register the units code digit in the same manner as previously described in connection with the registration of the tens code digit. 7

With the register relay 804 operated a pulsing circuit-extending from the second selector of Fig. 10 may be traced from battery, winding of relay 1004, back contacts of rotary magnet 1005, and vertical magnet 1003, inner right back contact of relay 1006, intermediate right back contact of relay'1007, conduc tor 1008, brush 923, next to outer right back contact of relay 909, intermediate right front contact of relay 907, conductor 908, outer right back contact of relay 809, back contact of counting relay 810, conductor 811, back contact of relay 601, winding of relay 602, inner left back contact of relay 600, left back contact of relay 603, conductor 604, left contact of relay 804, conductor 812, third posi- 7 tion terminal and brush 514 of steering switch 550, conductor 515, to groundat the outer left contact of relay 600. Relays 602 and 1004 energize in this circuit, relay 602 closing a circuit from ground at its front contact, over the right back contact of relay 605, conductor 606, brush 516 and the third position terminal of switch 550, conductor 517, right front contact of register relay 804, right back contact of relay 803, counting relay lead 813, right bacl: contact of counting relay 814, winding of counting relay 832 to battery. Relay 832 energizes and locks through the winding of relay 814, over the front contact of relay 832, to ground on conductor 508, but the relay 814 does not energize until relay 602 dee-nergizes and removes the shunting ground from its winding.

At the selector of Fig. 10 upon the energization of relay 1004 a circuit is closed for the vertical magnet 1003 from battery, through the winding of magnet 1003, the outer right front contact of relay 1000, to ground at the inner left front contact of relay 1004. Relay 1004 also closes an obvious circuit for relay 1009 which disconnects the tip and ring brushes of the selector during its vertical selective movement. Magnet 1003 energizes and at its contact opens the previously traced pulsing circuit through the winding of relay 1004 and the winding of relay 602. The selector switch is stepped vertically one step opening at the o-fi-normal terminal 1001, the

initial energizing circuit of relay 1000. Upon the opening of the pulsing circuit and the deenergization ofpulsing relay 602, the shunt around the counting relay 814 is opened and such relay energizes in the locking circuit of relay 832, extending the counting relay lead 813 over its front contact, back contact of counting relay 816, conductor 817, brush 518, and the third position terminal of steering switch 550, conductor 519, the right back contact of register relay 807, to battery through the winding of counting relay 818. Relay 818 energizes upon the next closure of the pulsing circuit and the consequent energization of relay 602 and locks through the windings of relays 802 and 810 in parallel, over the front contact of relay 818 to ground on conductor 508.

At the selector, relay 1004 reenergizes and in the manner previously described causesthe advance of the selector shaft another step again opening the pulsing circuit. Nhen the pulsing circuit is again opened and relay 602 deenergizes relays 802 and 810 energize, relay 810 opening the pulsing circuit extending as previously traced to the second selector and relay 802 opening the previously traced circuit extending through the winding of magnet 512. Magnet 512 now deenergizes advancing the brushes of steering switch 550 one step into engagement with the fourth set of terminals of the arcs access.

When the steermg switch leaves posi-' tion 3 the circuit of relay 504 is opened and such relay releases removing ground from conductor 508, thereby releasing the operated counting relays. A circuit is now established for advancing steering switch 550 into position 5 extending from battery, through the winding and back contact of magnet 512, the

to which they have V fourth position terminal and brush 514 of the steering switch, conductor 515to ground at the outer left contact of relay 600. With the steering'switch in position 5 a circuit is established for relay 505 extending from battery, through the winding of relay 505, the fifth posi terminal and brush 520 of the steering switch, conductor 521, to ground at the left back contact of relay 617. Relay upon energizing closes a circuit for magnet 512 preparatory to advancing the steering switch 550 into position 6. This circuit extends from battery, through the Winding of magnet 512 to ground at the front contact of relay 505. A circuit is also closed for relay 522 extending from battery, Winding of relay 522, the fifth position terminal and brush 503 of steering switch 550, to ground at the outer left contact of relay 501. Relay 522 upon energizing extends its own operating ground to relay 504 which thereupon energizes.

A circuit is also established for relay 607 extending from battery, through the winding of said relay, conductor 618, the fifth terminal and brush 514 of the steering switch, conductor 515 to ground at the outer left contact of relay 600. Relay 607 upon energizing looks over its inner right contact to ground on conductor 510, closes at its inner left front contact an obvious circuit for relay 603, at its outer right contact closes a circuit extending over conductor 619, to battery through the winding of relay 805 and at its next to outer right contact establishes a circuit eX- tending from battery, through the winding of. relay 620, contact of relay 607, inner right back contact of relay 610, right back contact of relay 614, left back contact of relay 609, to ground on conductor 510. Relay 805 at its right back contacts disconnects the code register relays 804, 803 and 803 from conductors of the group 331 extending to the operators position equipment and connects such conductors to contacts of the train of counting relays designated 825 in Fig. 8. Relay 804 now deenergizes. Relays 620 and 607 being now energized a circuit is established extending from ground at the front contact of relay 620, right back contact of relay 632, the intermediate left front contact of relay 607, conductor 333, brush 326, intermediate right contact of relay 325, inner right front contact of transfer relay 406, inner right back contact of transfer relay 412, winding of transfer relay 411 to battery. Relay 411 energizes closing a locking circuit for itself through its winding and the winding of transfer relay 402, the right front contact of relay 411 to ground on conductor 332, but relay 412 being shunted by ground on conductor 333 does not operate at this time.

It will now be assumed that the group of terminals which is selected by the second selector of Fig. 10 extending to the'distant office 122 comprises 40 trunks appearing in the second and third levels of the banks of the second selector and as, in response to the second code letter A, the switch shaft of the second selector has positioned its brush sets opposite the second level of each bank, the commutator brush 1011 will now be standing on commutator segment 1012. Should allof the trunks in the second level of both banks be busy there will be no ground potential connected to the segment 1012 and the circuit to be hereinafter traced from the brush 1011 through the right winding of relay 1000 Will not be effective to differentially release relay 1.000. As a consequence, with the steering switch 550 in position 5 and relay 603 energized, a circuit is completed from battery, through the winding of relay 1004, thence as previously traced through the winding of pulsing relay 602, the inner left back contact of relay 600, the left front contact of relay 603, the left back contact of relay 610, the right back contact of relay 614, the left back contact of relay 609, to ground on conductor 510. Relay 1004 energizes and again closes the previously traced circuit for the vertical magnet 1003 which in turn opens the pulsing circuit through the windings of relays 602 and 1004 just traced, relay 1004 in turn opening the circuit of magnet 1003. Thus magnet 1003 is operated and released to advance the switch shaft one step vertically to position the switch brushes opposite the third level of terminals in its banks.

At the sender, relay 602 upon energizing establishes a circuit from ground at its front Contact, over the right back contact of relay 605, conductor 606, brush 516 and its fifth terminal, counting relay lead 523, the back contact of counting relay 821 to battery, through the Winding of counting relay 829. Relay 829 energizes locking itself through the winding of relay 821, the front contact of relay 829, to ,round on conductor 508, but relay 821 does not energize until relay 602 deenergizes. When relay 602 deenergizes upon the operation of vertical magnet 1003, counting relay 821 operates. It will be assumed that when the second selector has stepped. to position its brush sets opposite the third level of its banks that the commutator brush 1011 encounters ground potential on the terminal 1018 corresponding to the third bank levels of the selector.

In F 1 the terminal equipment of two trunks extending to the office 122, both appea ing in jacks before the operator has been illustrated, the trunk 136, 137 being the first in the group of ten trunks appearing in the third level of the upper bank of the second selector, and trunk 126, 127 being the tenth in such group. In a similar manner ten other trunks extending to the office 122 appear in the terminals of the third level of the lower bank of the second selector. It

, Similarly so long as will be noted that so long as any trunk in this group is idle, ground will be connected to the commutator terminal 1018, over conductor 1019, the outer back contact of the cutoff relay of such trunk, for example relay 131, and over the outer back contact of the sleeve relay of such trunk, for example relay 130. any trunk in the other group often, one trunk of which is indicated at 1020, is idle, ground Will be connected to the conductor 1021 also connected to terminal 1018. Thus the brush 1011 upon encountering ground potential establishes a circuit from such ground, over brush 1011, right inding and inner right contact of relay 1000, the outer right back contact of relay 1006, the outer right back contact of relay 1007, conductor 1010, brush 924,0uter back contact of relay 909, outer right front contact of relay 907, conductor 910, inner right back contact of relay 809, conductor 613, right back contact of relay 600, next to inner right front contact of relay outer right back contact of relay 610, to battery through both windings of relay 609. Relay 609 energizes establishing a circuit for relay 614 from battery, winding of relay 614, front contact of relay 609 to ground on conductor 510. Relay 614 at its left contact shunts the left winding of relay 609, thereby reducing the resistance of the circuit previously traced through the right winding of relay 1000, so that the right winding of this relay receives sufficient current to cause the differential release thereof. Relay 1000 upon releasing opens the operating circuit of the vertical magnet to prevent further vertical stepping of the second selector.

Partial registration of tens digit of tmmlc mtmoer Relay 609 upon energizing opens the circuit of relay 620 which releases in turn opening the shunt around the winding of transfer relay 412 which now energizes in the locking circuit of relay 411. At its right back contact relay620 also prepares a circuit for relay S26, extendin from ground at the rightcontact of relay 522, right back contact of relay 620, conductor 828, to the lower armature of relay 843, this relay being now energized, however, since the second selector has taken but one vertical step and relay 843 releasing to complete the circuit above traced, through the winding of relay only when the selector takes more than five vertical step 1 nt this time the relays 413 to 416 inclusive of the tens trunk number registers are operated in accordance with the released condition of relays of the group Since counting relay 829 has been operated, relay 839 whose circuit extends from battery through the back contact of relay 829 to ground on conductor 508 is released and a circuit for register relay 416 is closed from battery winding of relay 416, outer left back contact of transfer relay 420, the outer left front contacts of transfer relays 412 and 406, the inner right front contact of relay 325, brush 327, conductor 555, the outer right front contact of relay 607, conductor 855, the back contact of relay 839, the front contacts of relays 840 to 847 inclusive to ground on conductor 50S. Belay 416 energizes and locks to ground over its lower winding and contact, conductor 418, outer right back contact of relay 205, conductor 322 to ground at the outer right contact of relay 325.

When relay 1000 deenergizes the circuit previously traced through relay 609 is opened at the inner right front contact of relay 1000 and relay 609 deenergizes in turn opening the energizing circuit of relay 614. Relay 614 being slow to release momentarily closes a circuit for relay 610 before it releases extending from battery, winding of relay 610., right front contact of relay 614, left back contact of relay 609 to ground on conductor 510. Relay 610 upon energizing looks over its inner left front contact to ground at the intermediate right front contact of relay 603, at its outer right back contact opens the initial energizing circuit of relay 609 and at its outer right front contact establishes a circuit for relay 615, extending from battery, resistance 1013, left back contact of rotary magnet 1005, inner right back contact of relay 1000, thence as traced to the next to inner right front con tact of relay 607, the outer right front contact of relay 610 to ground through the winding of relay 615.

Relay 615 upon energizing closes a circuit for relay 616, extending from battery, through the winding of relay 616, the left back contact of relay 605, to ground at the contact of relay 615, relay 616 looking to ground at the back contact of relay 602 and closing an obvious circuit for relay 617 which in turn closes a circuit for relay 605. Relay 605 upon energizing opens the initial operating circuit of relay 616, and relay 617 upon energizing opens at its left back contact the circuit for relay 505 which in turn deener gizes opening the circuit of magnet 512 to advance the steering switch 550 out of position 5 into position 6.

As soon as the steering switch leaves position 5 the circuit of relay 522 is opened at brush 503 in turn opening the circuit of relay 504. Relay 504 upon deenergizing unlocks the operating counting relays. With the steering switch in position 6, a circuit is established for the stepping magnet 512 extending from battery through the winding and contacts of magnet 512, the sixth position terminal and brush 514 of steering switch 550, conductor 515 to ground at the outer back contact of relay 600, causing the steerim switch to advance into position 7. A circuit is now established for relay 524 extending from bat- 

